Uniform pressure draw rolls

ABSTRACT

Uniform gripping pressure between two draw rolls for feeding a film web is achieved by providing three power cylinders along a movably mounted roll to press it into contact with the web and against a fixed opposed roller, and by providing a support yoke intermediate the ends of the opposed roller to counter the gripping force applied by the central power cylinder.

United States Patent Stock [451 July 25, 1972 [54] UNIFORM PRESSURE DRAW ROLLS 2,718,827 9/1955 Whittum ..100/17o x [72] Inventor: David K. Stock, Green Bay, Wis. FOREIGN PATENTS QR APPLICATIONS I 1 Assignefi FMC Corporation, 54111059, Calif- 747,347 4/1956 Great Britain"; ..226/l76 22 F! d: .4 l 7 1 1e Dec 9 0 Primary Examiner-Allen N. Knowles [21] Appl. No.: 95,282 Attorney-F. W. Anderson and C. E. Tripp 57 ABSTRACT [52] U.S. Cl ..226/l77, 226/194 l I 51 Int. Cl ..B65h 17/20 Uniform pp Pressure between two draw rolls for feeding [58] Field of Search ..226/l76, 177, 194; 100/170 9 film Web is achieved y Providing three Power cylinders along a movably mounted roll to press it into contact with the [56] References Cited web and against a fixed opposed roller, and by providing a support yoke intermediate the ends of the opposed roller to UNITED STATES PATENTS counter the gripping force applied by the central power lind 1,970,911 8/1934 1. Hartmann ..226/177 Cy er 3,! l9,324 l/l964 Justus ..l0 0/l70 7Claims,4Drawing Figures us 2 i L t J I! o n2 n2 no 100 Hz :0 f 1 I I06 0 l0 7 102 m 1 7 m 2 i JIW' 24 T: .111 20 23 Q W:

e 43 66 62 40 i6 34 6G 30 32 W" 52. 2; t

M H 1| 0 3-50 0 il 'Hh u-u u 54 pmmimaswn BEST AVAILABLE COPY 3.579.115

SHEI1UF2 ATTORNEYS |W| w Al -Uri Q. mm fi m-Fm K m m Qv m I m Ill .11 D

we Va B UNIFORM PRESSURE DRAW ROLLS BACKGROUND OF THE INVENTION The present invention pertains to web handling machines, such as bag forming or wrapping machines, and more particularly concerns a draw roll assembly for gripping and moving the web to or from other web handling mechanisms of the machine.

- Prior art gripping roll devices, such as are disclosed in US. Pats. to Rohdin 2,836,415 and Schjeldahl 2,947,345, are used for drawing off a web from a supply roll, or for feeding a web into a sealing head or the like. In either case the rolls may be continuously or intermittently driven, and some arrangement for controlling the gripping pressure is usually required. Moreover, it is always desirable to provide uniform pressure, even though the web may have localized areas of different numbers of plys, in order to maintain control of the web in a manner which prevents skewing and thus preserves accurate tracking.

Thus, in the Rohdin patent, supra, each roll comprises a series of short roll segments mounted on a common shaft of relatively small diameter, and, on only one of the rolls, means for applying pressure against the shaft between each longitudinally adjacent pair of roll segments. As stated in the Rohdin patent, the small diameter shaft and segmented construction provides the capability of accommodating localized variations in pressure between the two rolls because the shaft of-the pressure roll can flex without distorting its end bearings.

It is believed accurate to state that the basic concept of the patented Rohdin structure is the provision of a roll capable of substantial flexure intermediate its ends, and pressurized at close intervalsby means which will allow displacement at one or more segments of the roll to accommodate folded portions of the web, but which will correspondingly increase the pressure of the other segments of the roll. Stated otherwise, it is impossible to maintain absolutely equal pressure on a folded web gripped between the rolls of the Rohdin structure and it appears that the web, accordingly, will tend to skew and not maintain its linearity.

The Schjeldahl patent, supra, utilizes gravity for the gripping pressure between an upper and lower draw roll. Thus, the upper roll is mounted in vertically slidable end bearings, and the roll is coupled to a cross tie and other reinforcing structurewhich lends weight to the upper draw roll assembly. There is no provision for applying power pressure on the upper draw roll, although the gravity mode of operation does provide uniform pressure on a folded web gripped between the two rolls, and may thus prevent the web from skewing if the web folds have relatively thin plys. Thick web folds can lift the roll so that it is not parallel to the other roll, thus impairing accurate tracking of the web.

SUMMARY OF THE INVENTION Fluid operated power cylinders apply downward pressure on a vertically movable upper draw roll. The cylinders are connected to a common pressure line and are so dimensioned and arranged to maintain equal web gripping force in the nip between the upper draw roll and a lower draw roll. By providing support means for the lower draw roll at points vertically aligned with the cylinders, the lower roll is prevented from any undesirable flexure, and even a relatively thick web, regardless of the number (thickness) of folded plys across its width, is subjected to uniform pressure and maintains accurate tracking.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a transverse section through a typical bag making machine at a web gripping zone incorporating the improved FIG. 3 is a longitudinal section taken along lines 3-3 on FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT The draw roll assembly 10 (FIG, 1) of the present invention spans fixed frame plates I2 and 14 which in the present instance are part of a conventional bag making machine. FIG. I is viewed in the direction of web travel, or in a downstream direction, and the web path W (FIG. 2) is intermediate a fixed lower draw roll 16 and a vertically movable and air loaded upper draw roll 18. The lower draw roll is directly driven, and the upper draw roll is only indirectly driven by frictional contact with the web. Bearings at 20 and 22 in the frame plates 12 and 14 support the end portions of the lower draw roll 16, and in a known manner, a selectively engageable hand wheel 24 can be depressed to engage a keyway 26 in one end of a shaft 28 of the lower roll, and rotated to turn the roll during initial threading of the web. Similarly known construction includes a shaft extension at 30 which projects through the bearing 22 and carries a cog belt drive unit 32 for driving the lower draw roll, and which inboard of the bearing 22 has a gear 34 that drives a seal roll 36 (FIG, 2). The seal roll 36 and a seal bar unit 38 are part of attendant structure which does not directly concern the present disclosure of the draw roll assembly 10.

As best shown in FIG. 1A, the lower draw roll 16 comprises two sections which are centrally secured in coaxial relation by means including a stub shaft 40 on one roll section that is secured by a key 42 in a complementary bore of the other roll section. In order to securely fasten the two sections together, one hub portion 41 around the bore has a radial saw cut whereby a locking bolt 43 extending loosely through one half of the hub and threaded into the other half, clamps the hub onto the key and stub shaft. The stub shaft 40 merges with an integral bearing journal 44 that is seated in a central ball hearing 46. In turn, the ball bearing 46 (FIG. 2) is seated upon the upwardly facing arcuate end surface of a center yoke support 48 which is provided with slotted bolt holes for vertical adjustment relative to locking bolts 50. The bolts are threaded into the upstanding leg of a support bracket 52 which is bolted to a transverse tie beam 54 that interconnects the frame plates 12 and 14.

In order to assure firm frictional contact with the web and to provide a resiliently yieldable surface which minimizesthe effect of thickness variations in the web, the outer surface of the draw roll 16 comprises a resilient sleeve 55 provided with the usual circumferential grooves for fixed stripper fingers 60 that prevent the web from rolling around the draw roll. Each stripper finger is secured to a common mounting bar 62 that is bolted to frame blocks 66 on the frame plates 12 and 14. As shown in FIGS. 1 and 3, the upper end of each block is provided with a spring socket that holds a compression spring 70, the purpose ofwhich is later explained.

As thus far described, it is evident that the lower draw roll 16 is supported by the central yoke support 48 and the end bearings 20 and 22 to resist downward deflection, and that the same structural concept can be used with longer draw rolls to provide several points of support instead of only one central support.

Structural details of the upper draw roll 18 are the same as the lower draw roll, in that the upper roll is formed of two clamped-together sections (as in FIG. 1A), and includes a stub shaft 72 on the roll section which is secured by a key 74 in a complementary bore of the other roll section. An integral bearing surface 76 of the stub shaft is seated in a central ball bearing 78 that is aligned with the lower bearing 46. At each end, the upper draw roll 18 is provided with an axle 80, a ball bearing 82 which supports the axle, and a pivoted support arm 84.

As shown in FIG. 3, each support arm 84 is pivoted to the adjacent frame plate 12 or 14 by a pivot bolt 86. One purpose of such mounting is to provide upward pivotal movement of the upper draw roll to open the nip between the upper and lower draw rolls for initial threading of the web W. Thus, the compression springs 70 bear upward against the pivoted support arms 84, so that in the absence of downward pressure on the upper draw roll 18, the springs lift the pivoted support arms and the draw roll 18.

Circumferential grooves in a resilient outer sleeve 85 on the upper draw roll are aligned with the grooves of the resilient sleeve 55 of the lower draw roll and are each associated with a stripper finger 86. These strip er fingers are in fixed relation to the upper draw roll 18, and are thus mounted on a tie bar 88 that has end portions bolted to the pivoted support arms 84. Tie bar 88 is formed of three interconnected sections, end sections 90 (FIG. 1) which end short of the central bearing 78, and a center section 92 that is notched on its underside to clear a pivotally mounted pressure arm 94 which is aligned with the support yoke 48.

The pressure arm 94 is provided at one end with a downwardly facing arcuate surface which is engaged with the upper sector of the bearing 78, and at the other end has a pivot connection 96 to two depending arms of an overhead clevis bracket 98. The bracket 98 is bolted to a transverse bridge beam 100 which spans and is secured to the frame plates 12 and 14 by machine screws, one of which is shown at 102. Of cast or fabricated construction, the bridge beam 100 is provided with upstanding side flanges and lateral reinforcing webs to resist both longitudinal and torsional flexure. At points vertically aligned with the pivoted support arm 84 at each end of the upper draw roll, the bridge beam 100 is provided with a threaded boss 104 for mounting a fluid operated cylinder 106, the piston rod 107 of which rests in a top socket in the subposed support arm 84. A similar threaded boss 108 at the center of the bridge beam 100 mounts a fluid operated cylinder 110 with its piston rod 111 bearing down against the pressure arm 94.

Each cylinder 106 and 110 is of the single acting type and has a base inlet conduit 112 connected to a common manifold 113. In the absence ofa fluid pressure in the cylinder 110, and without sufficient pressure for the piston rods 107 to pivot the support arms 84 downward and overcome the force of the springs 70, the springs raise the pivot arms 84 and elevate the upper draw roll approximately one-eighth of an inch. This prevents the development of flat spots on the resilient surfaces of the draw rolls when the draw rolls are not in operation, and opens the nip between the rolls for initial threading of the web.

When the web has been threaded and the draw rolls are operating, the cylinders 106 and 110 are pressurized so that their associated piston rods react against the support arms 84 and the central pressure arm 94 in the expected manner, However, the central air cylinder 110 must apply more force than the end cylinders 106 in order to equalize the nip force along the rolls. One convenient manner of providing the necessary higher nip force to the center portion of the upper draw roll when commercially available cylinders do not provide the exact force ratio of central cylinder to end cylinders, is to select the nearest appropriate size for cylinder 110, and to proportion the length of the pressure arm 94 to provide the desired nip force. For this reason, the pivot 96 of pressure arm 94 is farther from the axis of the upper draw roll, than are the pivots 86 of the support arms 84. However, due to the very small amount of movement of the upper draw roll, the slight difference in pivot locations does not adversely affect the raising and lowering ofthe upper draw roll.

A similar effect can be obtained by using three cylinders of the same size, and reducing the pressure of the fluid supplied to the two end cylinders by means of a pressure regulator. in any event, the end result of the structure described is that equal nip force is produced along the entire nip of the upper and lower draw rolls because the central cylinder provides proportionately more force than the end cylinders, and because the lower draw roll is rigidly supported at points vertically aligned with the points of force application against the upper draw roll. Further, if the web being handled by the draw roll assembly has one or more longitudinal folds, the folded portions will cause a running deformation of the resilient sleeves 55 and where the web has increased plies due to the folds, because the nip force is uniform along the length of the nip. Thus, contrary to prior art teachings which allow lucalized roll deflection that alters the uniformity of nip pressure as in Rohdin 2,836,4l5, or which allow displacement of the roll as in Schjeldahl 2,947,345, the present draw roll structure maintains intimate and coextensive gripping engagement with the web. As a result, the present draw roll structure does not cause the web to veer, and provides accurate tracking of the web regardless of the variations it may have in the number of plies across its width.

From the preceding description, it is believed evident that the described results and advantages of the draw roll assembly 10 are due to providing plural equalized pressure applying means reacting against a rigid movable roll having a resilient surface forced thereby into pressure engagement with the resilient surface ofa fixed, rigid roll, and in the fixed roll having pressure resisting means aligned with the pressure applying means so that neither roll is materially deflected and uniform nip pressure and accurate web tracking is maintained.

Although the best mode contemplated for carrying out the present invention has been herein shown and described, it will be apparent that modification and variation may be made without departing from what is regarded to be the subject matter of the invention.

What is claimed is:

1. In a web handling machine a draw roll assembly for gripping the web comprising an upright frame plate at each side of the machine, a transverse bridge beam spanning said frame plates, a lower roll rotatably mounted between said frame plates, an upper roll displaceably mounted for downward engagement with said lower roll, a fluid operated cylinder mounted on said bridge for applying downward bias to each end portion of said upper roll, an intermediate fluid operated cylinder mounted on said bridge for applying a downward bias on said upper roll, a bracket depending from said bridge, and a presser arm pivoted to said bracket and extending under the piston rod of said intermediate cylinder above the path of the web, said presser arm having an arcuate undersurface engaged with a complementary upper surface of said upper roll to apply downward bias thereto without interference with the web.

2. Apparatus according to claim 1, and a fixed support yoke in supporting engagement with said lower gripping roll in opposition to said presser arm.

3. Apparatus according to claim 2, and a central annular bearing intermediate the ends of said lower roll, said fixed support yoke having an arcuate support surface engaged with said bearing but terminating below the path of the web, a second annular bearing intermediate the ends of said upper roll and defining said complementary upper surface engaged by the free end of said presser arm, said upper and lower rolls each comprising two coaxial sections separable in the plane of its associated bearing, one of said sections having a projecting, stepped shaft engaged with the bearing and keyed into a bore of the adjacent section.

4. Apparatus according to claim 3, and a pivot arm connected to each end of said upper gripping roll, means pivoting each arm to the adjacent one of said frame plates, a mounting bar interconnecting said frame side plates beneath the path of the web and intermediate the ends of said pivot arms, and a compression spring mounted between each pivot arm and said mounting bar, said springs applying upward bias to said upper roll for releasing gripping pressure and lifting said upper roll when all three of said pressure cylinders are deenergized.

5. In a web handling machine a draw roll assembly for gripping the web comprising an upright frame plate at each side of the machine, a transverse bridge beam spanning said frame plates, a lower roll rotatably mounted between said frame plates, an upper roll movably mounted for downward engagement with said lower roll, fluid operated cylinders mounted on said bridge for applying downward bias to each means for causing said central cylinder to apply proportionately more force than said end cylinders in order to maintain the linearity of said movable roll and produce a uniform gripping force along the nip of said fixed and movable rolls.

6. The machine of claim 5 wherein said presser arm is pivotally mounted on said bracket.

7. The machine of claim 6 wherein said bracket is a flat, platelike member. 

1. In a web handling machine a draw roll assembly for gripping the web comprising an upright frame plate at each side of the machine, a transverse bridge beam spanning said frame plates, a lower roll rotatably mounted between said frame plates, an upper roll displaceably mounted for downward engagement with said lower roll, a fluid operated cylinder mounted on said bridge for applying downward bias to each end portion of said upper roll, an intermediate fluid operated cylinder mounted on said bridge for applying a downward bias on said upper roll, a bracket depending from said bridge, and a presser arm pivoted to said bracket and extending under the piston rod of said intermediate cylinder above the path of the web, said presser arm having an arcuate undersurface engaged with a complementary upper surface of said upper roll to apply downward bias thereto without interference with the web.
 2. Apparatus according to claim 1, and a fixed support yoke in supporting engagement with said lower gripping roll in opposition to said presser arm.
 3. Apparatus according to claim 2, and a central annular bearing intermediate the ends of said lower roll, said fixed support yoke having an arcuate support surface engaged with said bearing but terminatIng below the path of the web, a second annular bearing intermediate the ends of said upper roll and defining said complementary upper surface engaged by the free end of said presser arm, said upper and lower rolls each comprising two coaxial sections separable in the plane of its associated bearing, one of said sections having a projecting, stepped shaft engaged with the bearing and keyed into a bore of the adjacent section.
 4. Apparatus according to claim 3, and a pivot arm connected to each end of said upper gripping roll, means pivoting each arm to the adjacent one of said frame plates, a mounting bar interconnecting said frame side plates beneath the path of the web and intermediate the ends of said pivot arms, and a compression spring mounted between each pivot arm and said mounting bar, said springs applying upward bias to said upper roll for releasing gripping pressure and lifting said upper roll when all three of said pressure cylinders are deenergized.
 5. In a web handling machine a draw roll assembly for gripping the web comprising an upright frame plate at each side of the machine, a transverse bridge beam spanning said frame plates, a lower roll rotatably mounted between said frame plates, an upper roll movably mounted for downward engagement with said lower roll, fluid operated cylinders mounted on said bridge for applying downward bias to each end portion of said upper roll, and an intermediate fluid operated cylinder mounted on said bridge for applying a downward bias on the mid-portion of said upper roll; the improvement comprising a bracket depending from said bridge, a movable presser arm, means for movably supporting said presser arm on said bracket with said arm extending under the piston rod of said intermediate cylinder above the path of the web, said presser arm having an undersurface engaged with a complementary upper surface of said upper roll to apply downward bias thereto without interference with the web, and means for causing said central cylinder to apply proportionately more force than said end cylinders in order to maintain the linearity of said movable roll and produce a uniform gripping force along the nip of said fixed and movable rolls.
 6. The machine of claim 5 wherein said presser arm is pivotally mounted on said bracket.
 7. The machine of claim 6 wherein said bracket is a flat, platelike member. 